31X6.75 Tire Size Guide

The 31X6.75 size uses a flotation-style format. In this code, 31 identifies the tire's overall outside diameter in inches, and 6.75 identifies the section width in inches. This size is built as a bias-ply tire and uses an inch-based rim system.

Unlike a modern P-metric size, the 31X6.75 does not directly spell out an aspect ratio in the code. Buyers read it primarily by overall height, section width, and wheel diameter, then compare those numbers to the vehicle's wheel openings, suspension clearance, and intended appearance. On antique and specialty vehicles, that simpler format is part of what keeps the size useful for restoration-minded fitment decisions.

The 31X6.75 fits a 5.0-inch wheel diameter, which is 127.0 millimeters. With flotation sizing like this, the leading 31 refers to the tire's outside diameter, not the wheel size, so the tire does not fit a 31-inch wheel.

Wheel diameter has to match exactly because the bead seats are designed for one specific rim size. Even when the overall height and width seem close to another tire, the 31X6.75 still requires the correct 5.0-inch wheel. Buyers should also inspect the actual wheel carefully on antique vehicles, since bead-seat condition and true dimensions matter just as much as the size marking itself.

The 31X6.75 is about 6.7 inches wide in section width, which is approximately 170.2 millimeters. Section width measures the widest inflated part of the casing from sidewall to sidewall rather than the tread face that contacts the road.

That difference matters during fitment checks. Tread width can be narrower, but section width is the number that usually causes interference with fenders, brake components, leaf springs, or steering parts. On a tall, narrow tire like the 31X6.75, buyers should evaluate both width and height together, because clearance problems can come from sidewall bulge as well as from the tire's 31-inch overall diameter.

The 31X6.75 has an outside diameter of 31.0 inches. In millimeters, that is about 787.4 mm. On this size format, that overall height is one of the primary numbers buyers use to compare stance and fitment.

Overall diameter affects several practical details at once. A tire this tall influences ride height, wheel-opening fill, and the visual proportions of an antique chassis. It also affects speedometer behavior whenever a substitute size is considered. If a buyer is trying to preserve the original look of a 1920s or 1930s vehicle, keeping close to the 31-inch height is often just as important as matching the width.

The 31X6.75 turns about 650.6 revolutions per mile. That figure comes from the tire's 97.39-inch circumference and gives a practical way to compare how this size rolls against another tire of different diameter.

Revolutions per mile matter whenever a buyer is considering a substitute size, because a taller or shorter tire changes how often the wheel turns over a given distance. On collector vehicles, that can alter speedometer and odometer readings as well as the visual stance. A replacement with a noticeably different revs-per-mile figure may still mount, but it will not behave exactly like the 31X6.75.

The 31X6.75 actually fits a 5.0-inch wheel diameter. The 31 in the size is the tire's overall outside diameter, while the wheel diameter is a separate measurement that must match the rim exactly.

This distinction is especially important with flotation-style sizes because the first number can look like a wheel measurement to buyers who are more familiar with modern radial codes. When restoring an older vehicle or servicing a specialty application, confirm the wheel itself before ordering any replacement. Matching the outside height alone is not enough if the rim diameter differs from the required 5.0 inches.

Yes, the 31X6.75 has documented use on late 1920s to 1930 vehicles, including Duesenberg and Packard applications, which places it firmly in an antique-era fitment context. Bias-ply construction also aligns with the kind of tire architecture commonly associated with earlier vehicles of that period.

Original-type fitment still needs to be verified against the exact vehicle, wheel, and body style involved. Antique cars often vary by trim, wheel manufacturer, and restoration history, so buyers should compare the current wheel size, tire clearance, and original specifications before assuming the 31X6.75 is correct. That careful check matters even more on vehicles being restored for judged authenticity.

Start with the wheel diameter, because the 31X6.75 only fits a 5.0-inch rim diameter. Next, compare the tire's 31.0-inch overall diameter and roughly 6.7-inch section width against the vehicle's available clearance at the fenders, suspension, steering, and bodywork.

Vehicle fitment depends on the complete wheel-and-tire system, not just the printed size. On antique and specialty vehicles, wheel age, prior modifications, brake conversions, and ride-height changes can all affect results. Buyers should also consider how the tall profile influences stance and wheel-opening fill, especially if they are trying to preserve a factory-style appearance rather than simply mounting a tire that seems close.

No, the 31X6.75 should not be treated as a broad catch-all replacement just because flotation sizing is often associated with truck and off-road use. This size also appears in antique vehicle contexts, and its 31-inch height, narrow 6.7-inch section width, and 5.0-inch wheel diameter make it more specialized than a modern all-purpose truck size.

Replacement decisions should account for wheel dimensions, body clearance, suspension layout, and the owner's goal for appearance and road behavior. A tire that is close in overall diameter but different in wheel size or casing profile can change both fitment and character. Buyers using the 31X6.75 on a restoration, specialty build, or older truck should compare the full package before substituting by height alone.

The 31X6.75 is a bias-ply tire, so its driving character is different from a modern radial. Bias-ply construction typically brings more sidewall movement, a more vintage steering feel, and a road manner that is closer to what antique and early specialty vehicles originally used.

Driving feel will still depend on suspension condition, alignment, wheel condition, load, and the age of the tire itself. On an older chassis, some owners value the authentic response and tall profile of a bias-ply casing, while others may be more sensitive to steering correction and tracking behavior. The 31X6.75 is usually chosen for period character first, with road manners evaluated in the context of the whole vehicle.

With a 31.0-inch overall diameter and a relatively narrow 6.7-inch section width, the 31X6.75 has a tall, narrow profile. That shape tends to give an antique vehicle a more upright visual stance and fills the wheel opening differently than a shorter, wider modern tire.

Ride and appearance are linked on a size like this. The tall casing can contribute to the period look many restorers want, while also affecting how the vehicle sits and how much sidewall is visible. If a buyer changes to a shorter or wider substitute, the result may alter not only clearance and speedometer behavior but also the proportions that make an early vehicle look right.

The 31X6.75 can be used on the road when the tire, wheel, vehicle condition, and intended use are all properly matched, but buyers should not assume it will behave like a modern passenger radial. Bias-ply construction and antique-era fitment expectations create a different driving experience that should be understood before regular use.

Road behavior depends on alignment, suspension wear, braking system condition, wheel integrity, and tire age just as much as on size. Before longer trips, inspect for cracking, air loss, cuts, or bulges and verify that the wheel and tire are appropriate for the vehicle's load and speed demands. Older vehicles running a 31X6.75 deserve a cautious, condition-first approach rather than a blanket assumption about modern-road performance.

The first quality check for the 31X6.75 is whether the tire matches the intended use of the vehicle. Because this is a bias-ply flotation-style size with antique-era applications, buyers should focus on sizing accuracy, casing consistency, wheel compatibility, and how faithfully the tire supports the vehicle's original proportions.

Construction quality matters most when the goal is predictable fitment and consistent behavior across a full set. A well-matched set of 31X6.75 tires should share the same overall dimensions, construction type, and intended service character. Owners of early collector vehicles often care as much about correct stance and visual authenticity as they do about ordinary replacement concerns, so the best choice is the one that suits the whole build.

Construction type matters because the 31X6.75 is identified here as a bias-ply size, and that affects both how the tire looks and how it drives. Bias-ply tires typically preserve the vintage sidewall profile and period road feel that many antique and classic owners expect.

Buyers choosing this size should decide early whether authenticity or modernized road behavior is the priority. On a restoration, the correct visual profile can be just as important as the basic dimensions, especially on a tall early fitment like the 31X6.75. Matching construction type across all four tires is also important, since mixing tire behavior can create uneven feel and inconsistent response on the road.

Yes, matching all 31X6.75 tires as a set is usually the better approach. Keeping the same construction type, overall diameter, and casing profile at every corner helps maintain consistent ride height, steering response, and appearance, particularly on antique vehicles with tall, narrow tires.

A mixed set can introduce differences in stance and road feel even when the printed size appears similar. Antique and specialty vehicles are especially sensitive to those changes because their suspension geometry and wheel openings were designed around narrower, taller tires. If one tire must be replaced individually, buyers should compare dimensions and construction carefully so the replacement does not stand out in either behavior or appearance.

The 31X6.75 should be inspected regularly for cracking, cuts, bulges, uneven wear, and slow air loss, even if the vehicle is driven infrequently. Bias-ply tires on antique vehicles can age out from time and environment long before tread depth alone tells the full story.

Time, heat, sunlight, moisture, and ozone exposure all affect rubber condition. Owners should look closely at sidewalls, bead areas, and tread surfaces before tours or seasonal driving, and any questionable tire deserves evaluation by a qualified tire professional. A collector vehicle that sees low annual mileage can still need replacement tires simply because age and storage history have changed the casing.

The 31X6.75 should be stored away from direct sunlight, heat sources, electric motors, and damp conditions when the vehicle is parked for long periods. Clean, dry storage helps preserve the rubber and casing shape on a bias-ply tire that may spend part of the year off the road.

Long stationary periods can also contribute to flat spotting and general aging, especially on older collector vehicles. If the car is stored seasonally, keep the tires properly maintained, inspect them before returning to service, and pay attention to any vibration or visible deformation once the vehicle is driven again. Storage care is part of preserving both appearance and roadworthiness in an antique tire setup.

The 31X6.75 should be checked on a routine schedule rather than only before major events. Regular pressure checks, visual inspection, and a close look for uneven wear are especially important on antique vehicles, where wheel condition, alignment, and long parked periods can all influence how a bias-ply tire behaves.

Pressure targets should come from the actual tire and vehicle guidance being used, not from assumptions based on size alone. Before each driving season and before any extended road use, inspect the full wheel-and-tire assembly for air loss, sidewall damage, and bead-area concerns. Catching a problem early is often the difference between preserving a usable vintage-style setup and replacing it unexpectedly.

The 31X6.75 should be replaced when age, cracking, bulges, cuts, repeated air loss, or visible casing deterioration make continued use questionable, even if tread remains. On antique and collector vehicles, tire condition matters more than mileage alone because time and storage history can age the rubber significantly.

Before any serious road use, inspect the full tire and wheel assembly carefully and compare what you see against the demands you plan to place on the vehicle. A tire can look acceptable at a glance yet still be too old or too compromised for dependable service. When there is any uncertainty, a qualified tire professional should inspect the tire before it returns to regular operation.

The most important checks are wheel diameter match, overall tire condition, air retention, and physical clearance throughout steering and suspension movement. Because the 31X6.75 is a tall 31.0-inch bias-ply size for a 5.0-inch rim, buyers should confirm that the entire wheel-and-tire system is appropriate before road use.

A practical inspection should include sidewalls, tread surface, bead area, and the wheel itself for damage or deterioration. Antique vehicle owners should also watch for rubbing at full steering lock and under suspension travel, since a tire this tall can fit statically yet contact body or chassis parts in motion. Careful inspection is especially important before highway-distance drives or tours.

Yes, buyers should review current sidewall markings, the vehicle's intended use, and any local road-use requirements before running the 31X6.75 in public-road service. Tire-size compatibility by itself does not answer every legal or practical question about how a vehicle should be equipped today.

Regulatory expectations can vary, and antique vehicles often operate under different usage patterns than modern daily drivers. Owners should also verify that the tire's condition, wheel compatibility, and load needs match the way the vehicle will actually be driven. A careful review of the complete tire-and-wheel package is the right approach whenever an older bias-ply fitment is being returned to road use.